1. Field of the Invention
The present invention relates generally to disc-stem connections and, more particularly, to apparatus for disc-stem connections in butterfly valves.
2. Description of the Prior Art
In recent years, industry has developed a need for moderately priced butterfly valve disc-stem assemblies which are strong enough to meet or exceed valve load requirements. The connection at the stem and the disc is often the weakest link in the assembly and therefore is a point at which breakdowns often occur when the valve is operating under pressure.
Various types of connections are known in the art but they are unsuitable to making a strong, rigid, properly aligned connection or too costly to be price effective.
A mechanical connection of the stem to the disc can be made by having slots on the stem and the disc that interlock with each other. This technique is shown in G. W. Hayden U.S. Pat. No. 868,182 and uses an interlocking slot connection with one stem on one side of the disc in a butterfly valve. The slot in the disc is made wide enough so that the connection has some play. A pivoting spur connection is employed on the other side of the disc. Accordingly, the disc is provided with enough latitude to self adjust itself into the valve body. The Hayden patent does not suggest how to make an industrial strength, rigid connection between the stem and the disc. And in fact, rigidity of the connection would defeat the essence of the invention. The patent also does not suggest how two valve stems connected in this way could be aligned with each other or to the center of the disc. The technique does not lend itself to producing valves strong enough for the desired industrial applications.
U.S. Pat. No. 3,539,148 shows an interlocking slotted connection but does not suggest any bonding of the connection, or any special techniques of bonding, or means for assuring accurate alignment of the stems, that would make the connection suitably strong for higher pressure industrial applications.
U.S. Pat. No. 4,688,594 shows how pins may be used to effect a disc-stem connection. This technique creates connections strong enough to be useful but is rather complicated so that the production price is undesirably high.
Consequently, a need exists for improvements in the art of making disc-stem connections for butterfly valves which will result in greater reliability and dependability at reduced levels of capital investment.